This invention relates to catheters, and in particular to variable stiffness magnetic catheters.
Magnetic catheters are catheters provided with a magnetic member by which the distal end of the catheter can be navigated (oriented and/or moved) by the application of a magnetic field. There are competing considerations in the construction of these catheters. The distal end must be sufficiently flexible to readily orient in response to the force applied by the magnetic field on the magnetic member while the lumen of the distal end must be sufficiently strong to resist kinking. However, the entire catheter must be sufficiently stiff to enable advancement through the patient""s body.
The present invention comprises a steerable magnetic catheter in which the flexibility varies along its length, and which preferably can be navigated without a guidewire. Generally, the catheter has a proximal end and a distal end, and a lumen extending therebetween. The catheter has regions of different flexibility along its length. There is a body, responsive to an applied magnetic field, and/or gradient, adjacent the distal end. The magnetic field and/or gradient may be applied with at least one stationary or at least one moveable magnet.
The body may be a permeable magnetic material, such as cold rolled steel or a permanent magnetic material such as neodymium-iron boron.
The distal end of the catheter is sufficiently flexible and the body is sized such that the catheter can bend at least 45xc2x0 in response to an applied field of 0.25T or less and more preferably at least 60xc2x0, and most preferably 90xc2x0 within about 5 mm of the magnetic member, which is typically at the distal end of the catheter. This allows navigation in small (less than 5 mm in diameter) vessels. The distal end is more preferably responsive to an applied magnetic field of 0.2T or less, and most preferably to an applied magnetic field of 0.1T or less.
As described above the catheter has at least two, and preferably at least three, regions of different flexibility. Each region is preferably of successively greater flexibility from the proximal end to the distal end.